1. Field of the Invention
The present invention relates generally to a wire structure of Chip on Substrate (COS) for layout detection and more particularly to traces of a ball-side surface connecting ball pads and bonding pads through holes to the wire of a die-side surface.
2. Description of the Related Art
BGA (Ball Grid Array) packages of the electronic and computer industries have been required to support higher lead counts within the same package footprint area. BGA packaging mainly includes a substrate which provides bonding pads for wire bonding and ball pads for ball soldering. The bonding pads and ball pads of the substrate are electroplated on its surface to prevent oxidization so as to increase the bondability and solderability so that a wire electrically connects all of the traces which connect to all of bonding pads and ball pads. In order to electroplate a metal layer on the surface of all of bonding pads and ball pads, all of bonding pads and ball pads are cathodes during the electroplating process. When traces of the substrate need to be checked to determine whether bonding pads connects to ball pads, we cannot use the socket of the test machine to detect the quality of an individual trace because all traces of bonding pads and ball pads are connected to one another by a wire resulting in a closed loop of all traces. Therefore, we must use an Automatic Optical Inspection device to detect quality of the traces of the substrate. This takes a long time to complete, thus substrate detection has the drawback of low efficiency. As shown in FIG. 1, a substrate 100 has a plurality of bonding pads 101 and a plurality of ball pads 102. The bonding pads 101 are located at the edge of a slot 110 of the substrate 100 for wire bonding, and the ball pads 102 are located at the periphery of the substrate 100 for ball soldering. Bonding pads 101 are connected to ball pads 102 to form a closed loop through traces 103 and holes 104. A wire 111 is electrically connected to the extensions of all traces 103 at the edge of the substrate 100. We must use an Automatic Optical Inspection device to detect traces of the substrate 100, because all bonding pads 101 are connected to the corresponding ball pads 102 by the corresponding wires 111 forming a closed loop. This takes a long time to complete so that substrate detection has the drawback of low efficiency.
As shown in FIG. 2, a substrate 200 has a plurality of bonding pads 201 and a plurality of ball pads 202. The bonding pads 201 are located at the edge of a slot area 210 of the substrate 200 for wire bonding, and the ball pads 202 are located at the periphery of the substrate 200 for ball soldering. Bonding pads 201 are connected to ball pads 202 to form closed loops through traces 203 and holes 204. A first wire 211 is provided at the edge of the substrate 200; a second sire 212 is provided in the slot area 210 and is electrically connected to the first wire 211 at the two ends of the slot area 210. The extensions of the traces 203 in the slot area 210 are electrically connected to the second wire 212 such that the traces 203, the first wire 211 and the second wire 212 form a closed loop. All bonding pads 201 are connected to all ball pads 202 through the first wire 211 and the second wire 212 because the traces 203 are extended to the slot area 210 for connection to the second wire 212. Therefore, slot sawing is performed at the slot area 210 to form an opened loop between the traces 203 and the second wire 212 such that the bonding pads 201 are connected to the corresponding ball pads 202 by the traces 203. The tensions of the traces 203 from the bonding pads 201 in the slot area 210 are too close one another and are not covered by solder mask such that the extensions are exposed on the substrate 200. Then when slot sawing is performed at the slot area 210, the ends of the extensions at the edge of the slot area 210 have lateral malleability and the substrate 200 is thereby broken down so that the adjacent ends are connected one another.
The present invention intends to provide a wire structure of substrate for layout detection in which traces of the ball-side surface of the substrate connect to ball pads and a wire of the chip-side surface of the substrate through holes. The wire is located at a slot area which is covered by solder mask to mount the ends of the traces to prevent a short of the traces after slot sawing. The present invention provides a wire connection to traces covered with solder mask in such a way as to mitigate and overcome the above problem.